This fixes a regression introduced by 87144036.

Thanks to Geoffrey Sechter and the Django NYC group for the report and Markus
for the review.

There is no need to wrap the save() call in transaction.atomic() as
it's already done down the call stack in Model.save_base().

Thanks to Trac aliases gerricom for the report, raphaelmerx for the
attempts to reproduce and Sergey Fedoseev and Tim for the review.

Refs #16891

Thanks Ben Kraft for the report, and Simon Charette for the review.

Thanks to bmispelon and uruz for the initial patch.

Thanks hop for the report and patch.

Thanks to Emanuele Palazzetti for the help.

The test creates and deletes a model in the same migration, and the model
had an AutoField. On Oracle, AutoField's are set up using deferred SQL, which
in this case was trying to modify a table after it had dbeen removed.

Referencing URLs by dotted path is a stronger convention than
importing the URLs.

Fixed #25672 -- Clarified why related ManyToManyFields with a custom intermediate model disable the remove() method.